Officially Official: the new McLaren P1

Forget the leaks and teases: here’s the full lowdown on the F1’s successor

So now we know how the P1, McLaren's long-awaited F1 successor, looks (well, mainly - this Paris concept is described as '95 per cent the same' as the car that'll go on sale next year). But Woking remains frustrating schtum on technical details, accompanying its Paris reveal of this decade's most hotly anticipated hypercar with a press release notably lacking in cold hard numbers.

But Top Gear has been delving behind the scenes, and knows more about the P1 than literally anyone else in the world (bar perhaps a handful of McLaren engineers, though even that may be debatable). Read on for the fruits of our delving, and a little informed speculation...

Though McLaren won't tell us what engine the P1 uses, it has confirmed its power-to-weight ratio will exceed 600bhp per tonne. The F1 - with its lissom 1140kg kerbweight and 627bhp V12 - developed 550bhp per tonne. The Veyron? Closer to 650bhp.

As the P1 uses the MP4-12C's wheelbase and carbon tub, we can reasonably assume it employs some iteration of the 12C's 3.8-litre twin-turbo V8 - no room for a V12, we suspect. So what does that mean for power? Well, we know the P1 has all manner of tricks to reduce weight - aluminium panels, lighter wheels and more - but we also know it uses a KERS system, which means it'll get a battery.

With heavy battery offsetting expensive lightweight materials, let's assume the P1 weighs the same as an MP4-12C: just over 1400kg. Which means, to achieve 600bhp per tonne, it'll have to make around 850bhp. If 100bhp of that is provided by the KERS, that means the V8 will need to generate about 750bhp. Hold on tight.

We know there's all sorts of clever aero going on, helping to generate over 600kg of downforce at speeds well below the P1's (as yet unrevealed) V-max. But the P1 boasts a slippery drag coefficient of just 0.34, because that gigantic rear wing tucks down into the rear deck at speed.

We know the P1 will be limited to a production run of just 500 cars: 100 more than the Enzo but barely half that of Porsche's upcoming 918 Spider, of which a coincidental 918 examples will reach the road.

And we know the P1 won't follow its predecessor's innovative approach to seating. While the F1 had room for three, with the driver front and centre, the new car features a conventional two-seat layout. Despite this passengerectomy, the P1 is nearly 30cm longer than the F1 - measuring 459cm from nose to tail - and 13cm wider. That means it's around 8cm longer and 4cm wider than the MP4-12C.

And the most important thing we know, wherever the P1's exact power output ends up, is that it'll be blisteringly, ridiculously real-world fast. McLaren isn't trying to outdo the Veyron on top speed, but instead to make ‘the best driver's car on road and track'.

The MP4-12C, remember, is the second-fastest car ever to lap the Top Gear test track, only eclipsed by the daft Ariel Atom 500. So how quick is the P1 going to have to go to put clear air between itself as its cheaper, commoner little brother? We can't wait to find out...

For the full story on the P1 and a stunning exclusive photoshoot, buy the November issue of TopGear magazine, on sale 10 October 2012